Evaluation of the Carcinogenic Potential of Bleaching Agents in a DMBA Induction-model.

Oral carcinogenesis is dependent upon cumulative effects within cells. Besides smoke, alcohol and solar radiation, many potentially carcinogenic noxious products in foods, medications andb the environment come into contact with the oral mucosa. Recently, a technique for bleaching vital teeth involving the application of 10% carbamide peroxide in trays by patients at home, the “nightguard vital bleaching technique,” has been introduced. Significant controversy has been generated over the risk of tissue damage from ingestion of carbamide peroxide during the bleaching process. In the current study, the effects of two bleaching agents, based on a 10% carbamide peroxide solution with and without Carbopol, were evaluated by the 9, 10-dimethyl-1, 2-benzanthracene (DMBA)-induction experimental model of carcinogenesis. For 20 weeks, 7 experimental groups were evaluated. Each group contained 10 hamsters and the following products were painted on the middle of the lateral border of the tongue: acetone, non-Carbopolcontaining 10% carbamide peroxide, Carbopol containing 10% carbamide peroxide, DMBA+10% carbamide peroxide with Carbopol, DMBA+10% carbamide peroxide without Carbopol, DMBA 0.5% in acetone and distilled water. The groups receiving acetone, 10% carbamide peroxide with and without Carbopol and distilled water showed no dysplastic alterations. In the group receiving DMBA alone, 4 animals developed dysplasias and 6 developed carcinomas, 3 being micro-invasive and 3 invasive carcinomas. For the group receiving DMBA and 10% carbamide peroxide with Carbopol, all 9 animals developed carcinomas, 2 being micro-invasive and 7 invasive. When DMBA and 10% carbamide peroxide without Carbopol was applied, 1 out of 9 animals presented intense hyperplasia and the other 8 invasive carcinomas. It was concluded that bleaching agents enhance the effect of other carcinogenic agents, probably by acting as promoters.